Several publications and patent documents are cited throughout the specification in order to describe the state of the art to which this invention pertains. Each of these citations is incorporated herein by reference as though set forth in full.
The use of metal nanoparticles (MNPs) in catalysis has rapidly increased in recent years because of their efficient and intrinsic size-dependent catalytic properties as well as their ability to catalyze a range of chemical reactions (Nishihata et al. (2002) Nature 418:164-167; Astruc et al. (2005) Angew. Chem., Int. Ed., 44:7852-7872; Moreno-Manas et al. (2003) Acc. Chem. Res., 36:638-643; Li et al. (2002) Langmuir 18:4921-4925; Ranu et al. (2009) Pure Appl. Chem., 81:2337-2354; Barbaro et al. (2010) Dalton Trans., 39:8391-8402; Migowski et al. (2006) Chem. Eur. J., 1:32-39; Durand et al. (2008) Eur. J. Inorg. Chem., 23:3577-3586). For many MNPs to catalyze reactions or result in efficient catalysis, the reacting substrates must directly interact with the metal surfaces. This metal-substrate interaction would be greater if the MNPs were synthesized “naked”. Unfortunately, however, atoms of “naked” MNPs have a greater tendency to aggregate into a bulk material due to their high surface energies, which results in loss of, or decrease in, their intrinsic catalytic activity and selectivity over time (Moulijn, et al. (2001) Appl. Catal. A: Gen., 212:3-16; Xing et al. (2007) Chem. Mater., 19:4820-4826). In particular, Pd nanoparticles (PdNPs), which are well known for their catalytic activities, can easily aggregate to form Pd-black because of the very high surface energy of palladium (Iwasawa et al. (2004) J. Am. Chem. Soc., 126:6554-6555). Although the degree of aggregation of PdNP or other MNP catalysts can be overcome or minimized by passivating the metals' surfaces with organic ligands, this too will, unfortunately, be accompanied by the loss of catalytic activity because the very sites on the metals where catalysis takes place will be covered by these surface passivating organic groups (Jayamurugan et al. (2009) J. Mol. Catal. A: Chem., 307:142-148). Accordingly, there is a strong need for efficient and recyclable nanocatalysts.